Electromechanical oscillator



y 1934- I N. DEIS'CH 1,965,280

ELECTROMECHANICAL OSC ILLATOR Filed June 15, 1 929 E'Sheets-Sheet FIG. 1

' [nvenfor July 3, 1934. N. DEISCH ELECTROMECHANICAL OSCILLATOR FiledJune 13, 1929 3 Sheets-Sheet 2 r. f m v m FIGS July 3, 1934. DEISCHELECTROMECHANICAL OSCILLATOR Filed June'l3, 1929 5SheetsS h eet 5 FIG.I0

FIG. 12

FIG. ll

CURRENT lawn/0r A I Patented July 3, 1934 ELECTRO EGHANIQAL QSQILLATQBNoel Deisch, Washington, D. 0. Application June 13, 1929, 51. 1 Ne.3?,666

8 Claims.

The invention relates to electromechanical 0s: cillators, especially tomeans of drive therefor, and is a continuation in part of my copendingapplication on Electromechanical oscillators filed April 16, 1928,Serial Number 270,546.

The general purpose of the invention is to pro-v vide means by which therate or frequency of vibration of the oscillator is rendered more nearlyconstant; its more restricted object, broadly stat- .ed, is to providemeans by which the periodic force which drives the oscillator isautomatically held in constant phase relation to the vibrations of theoscillator, and the value of this force automatically controlled in away such that the amplitude of vibration of the oscillator is heldconstant.

More specific objects relating to the construc.- tion, arrangement. andoperation of the apparatus involved in carrying out the invention willbecome apparent as the description proceeds.

Referring to the drawings;

Fig. 1 is a diagram showing a transparent, rod-shaped oscillator, anassociated optical SYS? tem by which the state of strain in theoscillator is automatically determined at selected phases of theoscillators vibration, light receptors or relays by which determinationsof the state of strain in the oscillator as expressed in optical valuesare converted into corresponding electrical values,

0 and electrical circuits and other electrical appara tus by whichdriving energy is supplied to the oscillator, its amplitude of vibrationcontrolled, and the phase relation of the driving force and of theoscillator vibrations maintained substantially .constant.

Fig. 2 is an enlarged view on the line 22 of Fig. 1, and shows thedirection of incidence of the light beam and its path through theoscillator.

Fig. 3 is an enlarged fragmental view of the alternating currentgenerator shown at 114 in Fig. 1, and shows means by which the angularposition of the stator coils of the generator may be varied relativelyto the field poles.

Figs. 4, 5 and 6 are fragmental views of the systerm illustrated in Fig.1, and show, together with the corresponding portion of Fig. 1, acomplete cycle of positions of the rotating mirror, during which the twolight beams are directed into corresponding receptors at appropriatephases of the vibration of the oscillator.

Fig. 7 is a diagram showing on a larger scale the angular disposition ofcertain optical elements of the apparatus illustrated in Figs. 1, 4 5and 6.

Fig. 8 is an enlarged perspective view of a type of optical om ensatorshown dia am a ly 4. in Fla 1.

F 9 is a a ram show n h p f rred ph se elat on etween the vib at ons o te oscillator a d the ph es of he. d ivin or F s. 10; shows the cfiect onhe. l ic t of the po a zed li h transmi ted y he a o ouced by di placemnt in oppos te d r ons long the ti t a sroue of corresponding nhasalpoint in he ib ation o th i la a optical. e erm n on of the s at o sraw; in the oscil ator ar mad Eis. 1.; sho s two series o o t ca c m hions. o st ain s the posi i n whic h ai wh n the ota n mirror is n cha esynchronism w h e os illa o s o he od. h mem or ach s r es bein ocat d@6 h t n he t m axis.

-ig- 1-3 sho s th alterat on i t e i ns of t t o s ries ct strain determnati n shown n Fig caused by a dep tu om phase y QBi-im- Fig. 13 shgwsthe positions of four series of optical determinations of strain, two ofthese series, 140, 141, situated on the line of zero displacement a andidentical with those shown in Fig. 11, being us d in fixing the positionof the oscillator with fer nce to he d i n fo ce. a w a itional series,142, 143, situated at opposite crests of vibr tion, being used, infixing the amplitude of b tion o he os illa r.

Fig. 14 shows a complete series of transformations from zero retardationto a retardation of one wave-length as they occur in ellipticallypotlarized light as produced in the strained os ci1 1a or.

Fig. 15 sh ws. trahsiormatioh in t state o retardation of polarizedlight transmitted by the oscillator and the compensator at variousphases of the motion of the oscillator under certain arbia trarilyassumed conditions of vibration, the sinoidal curve 132 representing themagnitude of the strain in the rod plotted against time, and the seriesof circles and vertical and horizontal lines at the left of the figurethe state of polarization of the emergent light at corresponding phasesof the vibration of the oscillator.

.16 shows. the saturation curve of a sample of iron such as mightconstitute the core 113 of he mutual inductance can 111 of Fig. 1, andillustrates the action oi the amplitude governor.

ne. o the actors on whi h the c a y of eriod at a osci lator dep nds isth a r ate amp ee f rce actin o the o cillator. and since the forcestending to maintain a constant frequency in an oscillating system varyinversely as the square of the damping coefiicient, it is important thatthis coefficient be reduced to the lowest possible value.

An inharmonic application of the driving force may be an importantsource of damping, and it may be shown that, ideally, the driving energyshould be communicated to the oscillator through the application ofaforce of sinoidal character held in the phase relation to the vibrationsof the oscillator shown in Fig. 9, where the curve 132 representssuccessive positions of one of the constituent particles of theoscillator on either side of its position of rest (represented by theaxis of abscissae 133) and the curve 131 represents the alterations inthe polarity and potential of the driving electromotive force (the axisof abscissae 133 here representing zero voltage) as plotted againsttime. 7

It will be seen by an inspection of this diagram that the curverepresenting the vibratory movement of the rod lags on the curverepresenting the driving electromotive force by 90?, the middle of theventral segments of the one having the same ordinate as the nodes oftheother. The maximum value of the driving forceoccurs at the point of mostrapid movement of the rod, the minimum algebraic value (whichcorresponds to the point of reversal of the polarity of the drivingforce) taking place-at the extremities of the period, when the rod ismomentarily quiescent, that is, at the middle of a ventral segment.- Theordinate of the driving force hence has its greatest algebraic value ata phase in the oscillation of the rod when the constituent particles ofthe rod are moving at their highest rate, and has its least algebraicvalue at a phase when these particles are moving at their lowest rate.

To achieve a constant rate the energy input should be free fromdisturbances in value, the shape of the curve representing the drivingforce should remain constant, and the phase relation of this curve tothe curve representing the rod vibrations should remain fixed.

The methods of drive hitherto employed in electro-mechanical oscillatorsfail to meet these exacting conditions. As respects the character--istics of the wave-form there is usually a wide departure from the idealsinoidal form just indicated. Each pulse of the driving current may infact be of such phasal length, or it may fall at such an epoch on thetime axis, as to overlap two opposed phases of the rods motion,therebyexerting a damping effect on the latter, and

though this damping effect will not be as great as the driving effect ofthe pulse, it will none the less introduce irregularities in the rate ofthe oscillator, and tend to set up oscillations in the latter which areharmonics of the fundamental oscillation. The energy pulse may alsosuffer variations of amplitude due to the fatigue of batteries or othercause, or itmay not be applied at the identical phasal position overlong periods,

notably through the fact that thermionic methods 'of amplification ascommonlynsed to. effect a drive are very sensitive to disturbance byslight.

and often uncontrollable changes in the constants of the circuit.

afford a degree of constancy in-the period ofthe oscillator ample formany pur'p'osesoflaboratory investigation, it is essential, incaseswhere the highest attainable degree of'precisionover long periods oftime is the object,-thatthe driving-en neeaeso ergy be applied andcontrolled in a way such as will satisfy the conditions above stated.

In this, as in my former application above referred to, the oscillatorin its preferred form consists of an elastic rod 15, Fig. 1, supportedat its nodal point, at 19, and oscillating freely along its longitudinalaxis at its lowest natural frequency. In my former application a methodwas described by which the frequency of the output of the electricaloscillation generator which supplied driving energy to the oscillatorwas controlled by an electrostatic coupling between the rod and theoscillation generator. A coupling of this type necessarily adds to theexternal damping of the oscillator, and in the present invention thissource of damping is entirely eliminated through the expedient ofproviding an optical coupling between the rod andthe oscillationgenerator.

The physical principles underlying the method by which this opticalcoupling is established will now be set forth.

It is well known that a stressed transparent body acts toward polarizedlight in the same way as a birefringent crystal, its optical behaviorbeing analogous to that of a negative crystal when the body is incompression and to that of a positive crystal when in tension, theoptical axis in each case being parallel to the direction of the appliedforce. An oscillating rod, then, in which there exists an alternatestate of tensional and compressional stress, is alternately positivelyand negatively birefringent, the effect being greatest at the nodalpoint of oscillation and decreasing progressively toward the ends of therod, where it is zero. Since the optical effects of extension andcompression are opposite and proportional to stress, the degree ofbirefringent of the rod is a periodic function of the time, equal phasesexhibiting equal double refraction.

Assuming a rod of adequate dimensions, and vibrating at sufficientamplitude, the elliptically polarized light emergent from the rod underconditions to be described will for each quarter oscillation (halfvibration) go through a cycle of complete transformations, changingthrough the series-plane polarized, elliptically polarized, circularlypolarized, elliptically polarized, plane polarized, etc.as diagrammed inFig. 14, which shows a complete series of transformations from zeroretardation to a retardation of one wavelength, and in Fig. 15, whichshows a number of complete transformations in apposition to the movementof the rod. (In the latter case the added retarding effect of acompensator is included, as explained hereafter.) Thus, if 113 Fig. 15be the trace of the motion of the rod about the position of rest,represented by the axis of abscissae 133, then the state of polarizationat the phase 144 will be as shown at 150, that is, the light will becircularly polarized. At the phase 145 the light will be polarized as at156, that is, it will be polarized in a vertical plane, at the phase 146the emergent light will be polarized as at 151, that is, circularlypolarized, etc. In other words the series of transformations shown inmore detail in Fig. 14 will be successively passed through, and thisseries will be repeated until the position of greatest strain,represented in the.

Though the methods of drive hitherto used mayown In Fig 15 by the pomt161 IS reached On the following quarter oscillation the series will ofcourse be traversed in reverse order. The same action takes place in thesecond half of the complete oscillation, that is, the part that lies'below the axis of abscissae. The number of trans formations shown isarbitrary, and will vary with the material, with the dimensions of therod, and with its amplitude of vibration. The above facts relating tothe optical properties of transparent rods in oscillation, in connectionwith the system of mechanical, optical, and electrical elements now tobe described, by which the momentary phase position of the oscillator isfixed through an optical determination of its internal strain, form thebasis of a method of establishing optical coupling between the vibratingrod and the generatorof an alternating E. M. F. which supplies drivingenergy to the rod in such way as to synchronize the motion of thisgenerator with the vibrations of the'rod.

Referring more particularly to Fig. 1, there is shown a source ofradiation 1 andmeans such as a monochromator 2 for selecting a certainrestricted region'of the radiation produced by the source 1. This sourcemay consist of a'mercury vapor lamp, and the monochromator may compriseaconventional arrangement of parts such as the restricting slit 3, thecollimator 4, the dispersing prism 5, the imaging lens 6, and theselecting slit '7. The transmitted radiation may '25- for'example berestricted to the line '4359Aof the spectrum of mercury vapor. The beamemergent from the monochromator 2 is collimated by the lens 8 and fallson thehalf-metallized mirror 9, by which a large part of the beam isreflected at'right angles and enters thepolarizer 11, the cylindricallens 13, the transparent oscillating rod 15, the cylindrical collimatinglens 21, the compensator 23, the analyzer 26, and the imaging lens 36,

4 which focuses it on successive facets of the rotating mirror 42.

through the analogous system comprising the polarizer 12, thecylindrical condensing lens 14, the oscillating rod 15,thecylindrical'collimating lens 22, the compensator 24, the analyzer 27,the

reflecting prism 41 by which it is in the illustrative construction bentthrough an angle of 67 and the imaging lens 39 which focuses it onsuccessive facets of the rotating mirror 42.

The polarizers 11 and 12, and the "analyzers 26 and 27, may' consist ofNicol prisms, the construction of which is well known. The polarizers 11and 12 are turned on their longitudinal axes through an azimuth of 45with respect to the longitudinal axis of the rod 15, whereastheprincipal'plane of the analyzers 26'and 27is desirably but notnecessarily held orthogonal with the axis of the rod, as shown. Thecylindrical lenses 13, 21, and 14, 22,'as shown in Fig. 2 are separatedfrom each other by a distance equal to their combined focal length,an'djar'e so' placed -'with-respect"to the oscillating rod that the axisof the latterc'oincides with the focal point of the lenses, tothe endthat the convergent and divergent beam is perpendicularly incident onthe air-rod interface so that refraction in the rod'does not occur andthe paths of all of the elements of the beam within the rodare of equallength. The compensators 23 and 24, whose purpose is to restore anelliptical vibration toa rectilinear vibration, or to'change a givenelliptic vibration to an elliptic vibration of different elliptic'ity,may be of the Soleil-Babinet type shown in detail in Fig. 8, consistingof a plane parallel'plate 122made of some doubly refracting materialsuch as quartz, 'whose optical axis "may be'taken as represented by thearrow 125,

and a split plane parallel plate composed of a wedge pair 123a and 123Dalso made of a doubly retracting material, and whose axes may be takenas represented by the arrows 126. The plate 1331) is adapted to bedisplaced in the direction or the arrow 127 by means of a micrometerscrew 25 (Fig. 1). The plate 122 is normally equal in its order to thewedge pair 123a, 1231) at-some intermediate thickness. The effectivethickness 0! the wedge-pair may thus be varied, causing a continuousvariation from positive to negative order in the transmitted polarizedbeam. compensator 23 will'normally be adjusted so that the polarizedlight incident on the analyzer 26 will be in the stateof polarizationshown at 150 in Fig. 15, that is, circularly polarized, when the rod isat rest, or when the instantaneous position of the particles of thevibrating rod is that shown by the intersection of the curve 132 withtheaxis 133 of Fig. 9. The adjustment of the second compensator 24 willdepend on the conditions of operation, and will be described farther on.

From theabove description it will be seenthat light will be transmittedin 'difierentamountsby the analyzers 26 and 27 at difierent epochs ofthe vibration of the rod, being fully transmitted at the epochscorresponding to polarized light 157, 159, etc. of Fig. 15, halftransmitted at epochs correspondingto polarized light 150, 151, etc.,and extinguished at epochs corresponding to polarized light 156, 158etc. There will result a series of transmissions of light through theanalyzer 26 at each oscillation, or more correctly a series offluctuations from zero, to maximum, to zero, etc., in the quantity oflight transmitted by the analyzer, in accordance with the relativeproportion of the two perpendicular components of the ellipticallypolarized monochromatic beam that at succeeding moments become incidenton the analyzer. There is thus afforded a means of determining the stateof strain inthe oscillator at any phase of its vibration.

That portion of the light beams 30 and 52 (Fig. -1) passed by theanalyzers 26 and 27 is, as above stated, focused on the faces of therota-ting mirror 42 by the lenses 36 and 39, respectively. As thismirror, which normally rotates in synchronism with the rod vibrations,sweeps around through successive positions, the beam 30 reflected fromthe mirror 42 passes successively into the collimators 35 and 37, bywhich it is transmitted to light-sensitive cells or relays representedhere by photoelectric cells 31 and 32. Similarly the beam 52 isreflected into the'collimators 38 and 40, and by them transmitted tothecells 33 and 34.

The facets of the mirror 42, the imaginglenses 36 and 39, and thec'ollimatinglenses '35'and 37,

the cells 33 and 34. The position on the curve- 132 representing thevibratory motion 'of the rod at which occur the momentary flashes whichenter the several photoelectriccells are shown in Fig. 13, where thesuccession of points 1) which enterthe cell 32 (Fig, 1). Likewise thepoints 142 and 143 respectively re giresenttl're 14s represent theportions of the beam 30 (Fig. 1')' which'ente'r the cells 31 (Fig. 1),and the points 141 representthe portions of the beam 30 (Fig.'

of Fig. 15, and the series 141 will acquire retar- 'plane, as shown at156 and 156, respectively.

portions of the beam 52 (Fig. 1) which enter the cells 33 and 34(Fig. 1) respectively.

In order to make clear the method by which these momentary flashes oflight from selected epochs of the vibration of the rod are utilized tocontrol the driving energy of the rod, it will be useful first tosimplify the conditions and to consider the action of a single one ofthese series of momentary radiation pulses. Such a series, equivalent tothe series 141 of Fig. 13 is shown at 141 in Fig. 10. It will be notedthat when these points are located on the axis 133, the lighttransmitted is circularly polarized, as shown on the arbitrary scale ofretardations at the left of this figure. If, however, the series beslightly shifted along the time axis in either direction, these selectedpoints at which light is reflected by the rotating mirror into thecorresponding photoelectric cells will move into regions of differentpolarization, as shown at 141, where the retardation is plus 1, and at141", where the retardation is minus 1. Such a shift along the time axiswould be caused by a departure from synchronism of the rotating mirror42 with reference to the vibrations of the rod 15.

In Fig. 11 are shown two series of points 140 and 141 at whichdeterminations of strain in the rod are made, the phase position of thetwo series of points being that which they occupy when the drivingcurrent and the rod are in synchronism. If now these two series ofdeterminations be shifted slightly along the time axis as shown in Fig.12, which corresponds to a lag of the rotating mirror, the series 140will acquire retardations corresponding, for example, to the point 145dations corresponding to the point 145 of Fig. 15. That is, the light inthe one series will be polarized in a vertical plane, and in the otherseries the light will be polarized in a horizontal Consequently thelight representing the series 140 will be completely extinguished in theanalyzer 26 (Fig. 1) and the light representing the series 141 will becompletely transmitted by the 'analyzer 26 and will proceed on to thephotoelectric cell 32. It is thus plain that a movement of the twoseries of points 140 and 141 along the time axis in either direction dueto a departure from synchronism of the rotating mirror 42 will cause adifferential change in the quantity of radiation that enters the twophotoelectric cells 31 and 32. This differential change, the sign ofwhich is fixed by the direction of displacement, is utilized to correctthe rate of rotation or phase position of the rotating mirror 42,

and simultaneously to correct the phase relation of the drivingelectromotive force to the vibrations of the oscillator, the correctionin question depending on the establishment of a photometric balancebetween the photoelectric cells concerned in the reception of the lightimpulses.

Referring again to Fig. 1, the oscillating rod 15 is shown as bearingconducting plates or armatures 16, in close apposition to which are heldelectrodes 17. The rod 15 is supported at 19,

which serves as the nodal point of oscillation, and the field plates 17are supported in correct relation to the armatures 16, by means shown indetail in my foregoing application on electrome- "chanical oscillatorsabove referred to.

- gthrough the secondary winding 112 of the mutual inductance coil 111and the lead 54 to the other terminal of the battery 28, the purpose ofwhich battery is to hold the opposed plates 16 and 17 under a certainelectrical bias. On an oscillating potential being developed in the coil112, attractions and repulsions are set up between the opposed plates 16and 17, which serve to drive the oscillator in a way detailed in myabove mentioned application. It will be noted that the oscillator 15comprises two aliquot portions 55 and 56, each of which portions may beconsidered as a separate oscillating member in that the oscillation ofeach portion is determined by its own physical characteristics and bythe node fixing action of the clamp or support 19. It is a feature ofthe present invention that energy may be supplied through the electrodes16 and 17 to each of these aliquot portions 55 and 56.

This oscillating electromotive force, which with the apparatus to bedescribed can be made to be of substantially sinoidal character, isgenerated in the secondary 112 of the transformer 111 through energysupplied by the alternator 114 which may consist of a conventionalconstruction shown in end elevation and in greater detail in Fig. 3,where a rotating field 106 consisting of a permanently magnetized bar orits equiva lent is mounted on and driven by the shaft 104, and thestator coils 107 are mounted on the turntable 121, by rotating whichlast the angular position of the stator coils with respect to the fieldpiece or rotor may be changed and the phase relation of the resultingcurrent to the phases of the rotation of the field piece and other partsconnected to the rotor shaft, that is, the phase coupling between thealternator and the oscillator, adjusted. As the rotor 106 turns, itsnorth and its south pole pass before successive pairs of the statorwindings 107, generating an alternating E. M. F. in the latter. Thestator coils 107 are connected through leads 108 to the primary winding109 (Fig. 1) of the mutual inductance coil or transformer 111.

The alternator 114 is driven by a motor 101, which derives its energyfrom the current source 102. A variable resistance 103 is provided bywhich the input of energy to the motor 101 may be adjusted. Mounted onthe shaft 104 of the motor 101 are, besides the rotor 106 abovementioned, the multiple-faced mirror 42 and the braking disk 105.Together, these comprise the rotating inertial system designatedgenerally at 115. It will be noted that the mirror 42 is shown at twopositions in Fig. 1, being shown in axial view in the upper part of thefigure and in plan view in the lower part of the figure. Thisduplication was made necessary by considerations of clearness in thediagram.

The electrical and mechanical system shown as enclosed by the brace 62represents an application of synchronizing and governing apparatusdescribed in detail in my copending application on electric cells 31 and32, it will be noted that these cells are connected in series, thecathode 48 of the cell 31 being connected by the lead 43 to the negativeterminal of the battery 44, andthe anrent curve of the tube.

ode 49 of the cell 31 to the cathode 50, of the cell 32, the anode 51being connected through the lead 45 with the positive terminal of thebattery 44.

With radiation of equal intensity entering the photoelectric cells 31and 32, which will be the condition when proper synchronism ismaintained. there will be an equal flow of current through the twocells, and due to the fact that. the intermittent beam will beintegrated in the cells due to the electrical capacity of the elec--trical elements comprising the lead 46 and the parts connected by it,the lead 46 will be held at a given negative potential. Suppose now thatdue to a shift of the mirror 42 from synchronism, the luminous fiuxactive in the two cells is diiferentially varied, so that a greateramount of luminous flux enters cell 32 and a smaller amount of fluxenters cell 31. The current flow through 31 is decreased and the fiowthrough 32 is increased, resulting in a lower negative potential activein the lead 46. Conversely, the opposite condition of relativeillumination results in a higher potential in the lead 46.

The potential active in the lead 46 controls the output of the amplifiercomprised in the brace 61, which may consist of a conventional groupingsuch. as the four-electrode thermionic vacuum tube 64. including afilament 68 heated by a battery 69. an accelerating grid 6'7 held at acertain positive potential by the battery '70, a shielding grid whichconnects with the lead 46, and the anode plate 66, held at a certainpositive potential with respect to the filament 68 by the source of E.M. F. 71. A high resistance 72 serves as a conducting link between theplate and the filament leads.

The output of the four-electrode tube 64 is amplified by thethree-electrode tube '73, whose grid '75 has connection in the platecircuit of the tube 64, as shown. The output circuit of the tube '73comprises the plate 74, one of the energizing coils of thecompound-wound braking electromagnet' 81, the current source 79, and theprimary coilv 78 of the mutual inductance coil or transformer 90.

The secondary coil 91 of the transformer 90 is connected across thefilament 88 and the grid 8''! of the amplifier 85. A biasing battery 77maintains the grid 8'7 of the tube at a potential such that. with noother electromotive force active in the filament-grid circuit of thistube, the value of the plate current corresponds approximately to themid-point of the grid-potential plate-cur- The filament-plate circuit ofthe tube 85 includes the current source 84, and the second magnetizingcoil 83 of the compound-wound electromagnet 81. The coils 80 and 83 areso connected in their respective 60 :circuits that the normal continuousflow of curriable resistance 103 is so adjusted that the input of energyto the motor 101 is in amount such that with equal illumination of thecells 31 and '32, and with a resulting median current flowing in theoutput of the amplifier 61, the braking action exerted by theelectromagnet 81 is just sufiicient to balance the frictional forces ofthe motor at synchronizing speed.

As above detailed, the potential active in the lead 46 acts through theamplifier 64 to control the current fiowthrough the output circuit ofthe amplifier 61, and it will be plain from considera tions developedabove that the value of the output current is greater for an angularlead of the mirror 42 and less for an angular lag of the mirror 42.Consequently the current flow in the magnetizing coil 80 of theelectromagnet 81, the magnetic flux cut by the disk 105, and the brakingforce acting to slow down the rotating system 115, which includes theinultifaced mirror 42, are all in the same sense greater for a lead ofthe mirror 42 and less for a lag of the mirror 42. In other words, whenthe system is in such relation that the series of points of straindetermination 140 and 141 are as shown in Fig. 11, the braking force hasa median or normal value, when the series of points occupy the positionshown in Fig. 12, the braking force has a lower value, and when theseries of points are displaced along the time axis in a directionopposite to that shown in Fig. 12, the braking force has a higher value.This action of the rotating system in which a force (represented by thedriving force of the motor) is applied, tending to cause the movingsystem to depart from synchronism by taking on a faster rate ofmovement, and a second force (represented by the braking force exertedon the disk 105) is applied, tending to cause the moving system todepart from synchronism by taking on a slower rate of movement,-thevalue of the latter force a being automatically controlled, tends tohold this system in synchronism with the rod vibrations, and to hold thedriving energy in the relation shown in Fig. 9. (The term synchronism isused here as implying that the periods of the various phenomenaconcerned are either the same, or are simple multiples or submultiplesof each other, though not necessarily that there is phase coincidencebetween any of these phenomena.)

It may be stated here that the synchronous speed of the rotating system115 including the mirror 42 will depend on the number of facets in themirror 42, each facet corresponding to a complete oscillation, and thatthe number of stator coils 107 in the alternator 114 will be determinedby the number of facets in the mirror4z.

It is a well known fact that where an inertial system such as therotating system 115 of the motor 101 is subjected by a stabilizingapparatus to a correcting force tending to return it to a certaindesired fiducial position, such as a position cor-responding to a givenphase relation or to a position of equilibrium, the impetus given theinertial system in theprocess of returning it to the desired positioncauses the inertial system to pass beyond this position. In this secondposition of displacement the inertial system is again acted on by acorrecting force tending to return it to the normal position: It againacquires kinetic energy and is again carried beyond the desiredposition, and thisaction continues. This oscillation of the inertialsystem over a certain amplitude on either side of the correct position,known as hunting may in certain applications be very persistent andobjectionable.

In the present invention hunting of the local system is obviated by anapplication of methods developed at length in my two applications forpatent on synchronizing apparatus, above referred to, in which apparatusmeans are provided whereby the force resisting a displacement of theinertial system from the correct phasal position is of many times thevalue of the force tending to return the system to this position. Anyovershooting of the inertial system due to accumulated kinetic energy israpidly arrested, and, when the inertial system is brought to a halt, amuch smaller force acts to return the system to the normal phaseposition, and hence the kinetic energy accumulated during the movementof return is correspondingly smaller. The oscillations of the in rtialsystem in establishing an adjustment thus possess a very steepdecrement, however large the forces applied in maintaining anadjustment, and the synchronized system maintains a correspondinglyclose phasal relation with the system to which it is synchronized.

The components particularly involved in the device for preventinghunting are the transformer 90, the amplifier 85, the current source 84,and the coil 83 of the compound wound electromagnet 81.

In following the correcting action of this system of elements, assumethat the rod vibrations and the mirror revolutions are in propersynchronism. A substantially constant current of some certain value isthus flowing through the winding '78 of the mutual inductance coil 90and the windin of the braking electromagnet 81. No induced current isflowing in the secondary 91 of the transformer 90; a certain mediancurrent is hence flowing through the coil 83, which acts with thatflowing in the coil 80 to produce a certain flux in the brakingelectromagnet 81, resulting in a speed of the motor 101 which results inproper synchronism.

Assume now that through some transient cause the rotating inertialsystem 115 of the motor 101 is slightly retarded. A smaller currentflows through the output of the amplifier 61, decreasing the flux in thebraking coil 80, and the motor rotating system 11 tends to increase itsspeed and to take up a position of advance. Simultaneously with thedeparture from the correct phasal position there is a drop in the valueof current flowing in the primary winding 78 of the transformer 90, andan E. M. F. is induced in the secondary 91 of the latter. The connectionof the secondary winding 91 with the filament 88 and the grid 87 of thetube is such that this induced E. M. F. acts to reinforce the E. M. F.of the biasing battery 77 and thus to decrease the normal flow ofcurrent through the output of the tube 85, as also through the coil 83,and to reduce the braking action exerted on the disk 105. In otherwords, the altered flow of current in coils 80 and 83 caused during thepried of retardation of the inertial system 115 acts individually andadditively to prevent further retardation or departure from the normalphase position.

As soon as the motion of departure has been halted, however, no furtherchange occurs in the density of current flowing in the primary '78 ofthe transformer 90, the E. M. F. generated in its secondary 91 falls tozero, and the current flowing through coil 83 regains its normal value.However, the current flowing in coil 80 still has a lower value than thenormal value, due to the lag from the correct phase relation, and thereduced braking action tends to cause the system to begin a motion ofcorrection toward its normal phase position. As soon as this motion ofrecovery begins, the current flowing in the output circuit or" theamplifier 61, which includes the coil 80 and the primary '78 of thetransformer 90, increases, and an E. M. F. is induced in the secondary91 of the transformer 90, the polarity of which E. M. F. is opposite tothe polarity of the E. M. F. which had been induced during the motion ofdeparture. The biasing action of the battery 7'7 is hence in this caseopposed, and more than the normal current is allowed to flow through thecoil 83. The action of the coil 80 tending to return the rotating systemto the desired phase position is thus opposed and partially balancedout, and this restraining action of the coil 83 on the coil 80 continuesthroughout the period of return to the normal or fiducial position. Themotion of recovery must therefore take place slowly as compared with themotion of departure.

From the above it is seen that, during the period of retardation of therotating mirror due to the action of a disturbing force, the coil 83acts to assist the coil 80 in preventing the retardation, but during theperiod of recovery the coil 83 acts to resist the action of the coil 80.In other words, the force opposing a departure from the normal phaseposition, when that departure is in the direction of a retardation ofthe rotating system 115, is much greater than the force tending toreturn the system to the normal phase position.

An analogous action takes place when the departure is in the directionof an advance from the normal position. During the period of departurethe current flow in the output of the amplifier 61 increases and thatportion of the braking effect caused by the flux generated by the coil80 is likewise increased. Coincidently with the departure, an E. M. F.is induced in the secondary 91 of the transformer which tends to opposethe E. M. F. of the biasing battery 77; the current in the coil 83 isthus also increased. The coil 80 and 83 thus both act during the periodof departure from the correct phase position to prevent the motion ofdeparture. When the departure ceases, the current in coil 83 returns toits normal value, whereas the current in the coil 80 remains at a highervalue than normally, and tends to increase the braking of the disk 105and so to bring the system 115 back to its normal phase position. Assoon as the motion of return toward the correct phase positioncommences, however, the current in the circuit including the coil '78decreases, an E. M. F. is generated in the coil 91 which assists thebiasing action of the battery 77, and the current in the coil 83 of thebraking electromagnet 81 is decreased.

From the above it is clear that when a departure from synchronismconsisting either of a lead or a lag from the desired phase relationoccurs, the braking electromagnet coils 80 and 83, which controlindependently variable components of the correcting force, assist eachother during the period of departure and oppose each other during theperiod of recovery. This is a condition conducive to great stability inthe rotating system, and the latter will hence suffer displacementsthrough only a very small angle on either side of the desired phaseposition. When the azimuth of the field coil turntable 121 (Fig. 3) hasbeen adjusted to such an angular position with respect to the facets ofthe mirror 42 that the phase relation of driving force and oscillatorvibrations are as shown in Fig. 9, the apparatus thus far detailed willoperate to maintain this phase relation as long as the oscillator is inoperation.

In order to ensure that the decrement in the oscillating rod remainsconstant it is necessary that the amplitude of vibration of the rod beheld drive the oscillator.

constant, regardless of external conditions or changes in the constantsof the driving circuit. In the present invention this is accomplishedthrough optical means closely analogous to those just described inconnection with the control of the phase position of the driving force.The series of strain determinations here concerned are those shown at142 and 143 of Fig. 13, and occur, as will be seen, at opposite crestsof the vibrations. Selections from the light beam 52 are made at thesepoints by the mirror 42, as above detailed. In the illustrativeconstruction shown, light from the series 142 enters the cell 33 andlight from the series 143 enters the cell 34. In the normal operation ofthe oscillator, the light at the terminal crests of the vibrations iscircularly polarized, as shown at 155 and 155 in Fig. 15. The cells 33and 34 are thus normally equally irradiated, the lead 4'? is held at agiven potential, and the current output of the amplifier 63, whoseconstruction is similar to that of the amplifier 61, is held at a givenlevel. If the amplitude of the rod be assumed to fall to the point 162,162' of Fig. 15, corresponding to radiation ofj the character indicatedat 160, 160', respectively,

more radiation enters the cell 33, less radiation enters the cell 34,the potential of the lead 47 is lowered, and the current output of theamplifier 63 is lowered. The converse action takes f1 place if theamplitude of the rod is increased.

The current output of the amplifier 63 passes into coil 110, whichconstitutes a separate winding on the transformer 111. As above stated,the alternating current produced by the dynamo stator coils 10'7 flowsthrough the primary winding 109 of the transformer 111, producing analternating change in magnetic flux in the core 113, the result beingthe generation of an alternating potential in the secondary coil 112,which acts harmonically on the electrodes 16 and 1'1 to The effect ofthe variation of current in the coil 110 on the potential of thealternating current supplied to the driving electrodes 16 and 17, onwhich depends the amount of driving energy supplied to the rod 15, willbe made apparent by an inspection of the diagram, Fig. 16, whichrepresents the saturation curve of a sample of low carbon silicon iron,such as might constitute the core 113 of the transformer 111, (Fig.

1), the magnetic flux density being plotted as ordinates against theexciting current.

Assume that the greatest value of current that can be passed by theamplifier 63 (Fig. 1) and delivered to the winding 110 to be that shownat 180 (Fig. 16), which sufiices to raise the sat uration curve of thecore 113, (Fig. l), to the point 170, (Fig. 16). Assume also that thenormal working point of the amplifier 63 (Fig. 1) is the point 179 (Fig.16) and that this point of saturation is, normally, continuouslymaintained by the action of light reaching the photoelectric cells 33and 34, (Fig. 1).

Assume further that the sinoidal current flowing in the coil 109(Fig. 1) represented by 1'75 (Fig. 16) superposes a magnetic change offlux density comprised between the abscissae 1'13, 174 on the normalmagnetization due to the current flowing in the coil 110. This will thenlead to the generation of an alternating E. M. F. in the secondary 112having a certain value. If now an increase of current in the coil 110due to an increase of amplitude in the rod vibrations lift the level ofsaturation in the core 113 (Fig. 1)

- to the point 181 (Fig. 16) then the cyclic difference of saturationdue to the periodically fluctuating current 175' flowing in the coil 109(Fig. 1) will have fallen to the value comprised between the abscissae171, 172 (Fig. 11) and the potential of the alternating driving currentin the secondary 112 (Fig. 1) and consequently the driving effect onrod, will have fallen to a correspondingly smaller value. Conversely adecrease of current in the coil 11.0 (Fig. 1) caused by a fall inamplitude, will have the efiect of increasing the driving E. M. F.produced in the secondary 112. In either case the departure of the rodfrom the correct amplitude is corrected.

It will be of advantage from the point of view of sensitiveness that theiron of which the core 113 Fig. 1 is constituted be of a kind such thatthe break in the curve of saturation is rather abrupt, and that theamplifier 63 have a fairly steep characteristic.

The amplitude of beat of the rod can be changed after the rod has beenset in motion from one value to another to suit a predetermined ordesired value by adjusting the compensator 24 (Fig. 1).

Since the inertia of the entire optical and electrical system ofcorrection in the amplitude governor just described is very small ascompared to that of the oscillating rod, and since the energy suppliedto the rod in returning it to a given position of amplitude will nottend to take it beyond that position, there will be a total absence ofhunting- The effect on amplitude caused by the very small departuresfrom synchronism that may take place in the rotating mirror 42, whichdepartures must for reasons above explained necessarily be confinedwithin the region separating two areas of oppositely plane polarizedlight, and will practically be confined to a small portion of such achange, will have only an infinitesimal effect on the amplitude, for thechange of phase effects in the polarized radiation for a givendisplacement on the time axis is smallest at the crests of thevibrations, represented by the points 142 and 143 on the curve 132, 13,and greatest at the points 140 and 141 at which this curve cuts the axisof abscissae.

The totality of apparatus above described, in short, acts to control themotive parameters of the driving force (i. e., both the phase relationof this force to the oscillator vibrations and its effective intensityas a driving agency) by means which do not in any way depend on acoupling involving an exchange of energy between the oscillator and thegoverning apparatus which controls these motive parameters.

In starting the oscillator, or initiating its vibration, the rotatingsystem 115 is allowed to gain speed from a position of rest until theelectrical oscillations produced in the coil 112 comes to consonancewith the natural period of the rod, when the latter will begin tooscillate, and the rotating system will be held automatically in aposition of synchronism.

While I have described my invention in detail with respect to thepreferred form thereof, I reserve the right to make such changes in thedetails of construction or such substitution of equivalents as conformto the spirit of the invention or fall within its scope as defined inthe appended claims. It is moreover not indispensable that all featuresof the invention be used oonjointly, as they may be advantageouslyemployed in various combinations or subcombinations.

I claim:

1. A body capable of oscillation, means for applying a motive force tocause said body to oscillate, means controlled by said body to vary thecharacteristics of a beam of radiation according to the phase positionof said oscillator, and means by which radiation corresponding tocertain phases of oscillation of said body control motivecharacteristics of the applied force.

2. An oscillator, means to supply a periodic driving force to saidoscillator, optical means for determining the momentary phasal positionsof said oscillator, and means responsive to the value of saiddeterminations to control the phase relation of said driving force.

3. A transparent oscillator, means for supplying driving energy to saidoscillator, means for passing radiation through said oscillator, andmeans responsive to changes in the character of said radiation caused bythe oscillation of the oscillator to control said driving energy.

4. An oscillator, means for applying driving energy to said oscillator,generating means for producing said driving energy, and means controlledby said oscillator and active on said generating means to vary the phaserelation of the oscillations of said oscillator to the cycles of saiddriving energy.

5. A body capable of oscillation, means for generating a driving forceto cause said body to oscillate, said generating means including aninertial system moving substantially in synchronism With said body,means for determining momentary phase positions of said body, and meansresponsive to said determinations to control the movement of saidinertial system.

6. In a periodic system comprising an oscillator and a moving inertialsystem normally held in substantial synchronism with said oscillator,the improvement characterized by means for applying a force tending tocause said moving system to depart from synchronism by taking on afaster rate of movement, means for applying a second force tending tocause said inertial system to depart from synchronism by taking on aslower rate of movement, and means controlled by said oscillator to varyone of said forces to maintain said moving inertial system insubstantial synchronism with said oscillator.

7. A transparent oscillator, means for passing a beam of polarized lightthrough said oscillator, optical analyzing means to extinguish saidpolarized light as a function of the phase position of said oscillator,receptors to convert the energy of said light into electrical energy,means to direct said light into said receptors according to the phasesof said oscillator, means to generate energy to drive said oscillator,and means associated with said receptors to control said energygenerating means.

8. The method of controlling the oscillation of a mechanical oscillatorwhich consists in generating electrical oscillations, producingmechanical oscillations by means of said electrical oscillations,altering a stream of radiation by means of said mechanical oscillations,and controlling the characteristics of said electrical oscillations bymeans of said altered stream of radiation.

NOEL DEISCH.

